Earphones, especially canal-type earphones, which are used closely in the user's ears, become a major cause of hearing loss of the user in the case of reproducing an excessive sound pressure at high frequencies.
In order to solve the foregoing problem, a resonance space is provided in an earphone using the principle of a Helmholtz resonator, such that it acts as a sound absorption circuit in the Helmholtz resonance region to reduce a sound pressure level.
US 2016/0066111 discloses an earphone using the principle of the Helmholtz resonator. Referring to FIG. 1, an ear canal earpiece 1100 includes a sound converter 1110, first to third sound guide units 1120, 1130 and 1140, and a sound barrier 1150 positioned in the region of the third sound guide unit. In addition, the earpiece includes a Helmholtz resonator 1170 in the sound barrier 1150. The Helmholtz resonator 1170 includes a first open end 1171 facing the ear and a space 1172 positioned away from the ear.
The Helmholtz resonator includes an element 1173 that forms an acoustic mass and the space 1172 that is blocked. The Helmholtz resonator acts as a sound absorption circuit, and thus reduces a sound pressure level inside the ear canal in the Helmholtz resonance region.
However, the earphone using the principle of the Helmholtz resonator has a disadvantage in that the whole earpiece should be replaced to change the resonance point of the Helmholtz resonator because the Helmholtz resonator is disposed in the earpiece.